This invention relates to controlling noise propagating from a gas turbine engine, and, more particularly, to controlling noise by effectively altering the nozzle exit area.
Gas turbine engines are widely known and used for power generation and vehicle (e.g., aircraft) propulsion. The engine produces engine noise due to the airflow moving through the engine and the various moving components within the engine. A person within the aircraft cabin may hear the engine noise. A person living near to an airport may often hear engine noise from the aircraft taking off and landing at the airport. Community noise is ordinarily defined as the aircraft noise perceivable by people located on the ground in the vicinity of the airport. Engine noise may limit an aircraft's ability to land at certain airports after certain hours, causing loss of revenue for an airline.
Noise from the engine primarily propagates fore and aft of the engine. The frequency content of the noise includes a tonal component and a broadband component. The fan section of the engine is a major contributor to overall engine noise, especially the tonal component. The size of the fan section relates, in part, to the desired bypass ratio for the engine, which is the ratio of fan bypass flow to core engine flow. The trend in commercial aircraft has been to increase the bypass ratio of the engine. However, increasing the bypass ratio generally requires increasing the size of the fan section within the turbofan engine, which may increase the noise contribution of the fan section.
What is needed is a method of optimizing engine noise for various flight conditions while maintaining engine thrust.